Heating, ventilating and air conditioning (HVAC) systems have been developed with multistage furnace sections, as well as multistage cooling sections, for improved efficiency and improved comfort for the occupants of the space being conditioned. With regard to multistage furnaces, for example, initially two stage furnaces were developed but furnace designs have evolved into three stage types which are capable of producing heat at low, medium and high output settings.
The retrofitting of multistage air conditioning systems into existing facilities with single stage thermostats, or thermostats with fewer stages of control signal capability than the capability of the air conditioning system itself, has presented problems for installing HVAC systems in existing facilities, for example. However, HVAC systems with controllers and methods of operation in accordance with the present invention have overcome such problems of the prior art.